Such a luminaire is known per se, for example from the published patent application WO 2008/146229, filed in the name of Applicant. The luminaires described in said patent application comprise a plurality of illumination systems, each having a housing, a light source, an exit window and reflecting means. In the embodiment shown in FIG. 3-C, a collimating plate is provided on a wall of the housing. This plate consists of an optically transparent sheet having a plurality of elongated linear prism structures with right top angles. This sheet is intended to redirect light beams impinging at grazing angles towards an angle closer to the normal to the sheet. In the known luminaire, especially light emitting diodes (LEDs) are used as a light source. During operation of the luminaire, such LEDs emit Lambertian light in the direction of the collimating plate, aiming to transform the LED luminance from a very high and discrete degree to a uniform degree of brightness which is acceptable to an observer.
Although said luminaire presents a clear improvement as compared with the known prior art luminaires, the described luminaire still has as a drawback that it does not fully comply with current strict glare requirements. Glare is caused by excessive contrast between bright and dark areas in the field of view of an observer. Illumination systems and luminaires comprising LEDs are known to cause glare problems. Especially in the design of illumination systems and luminaires intended for application in the area of in-house lighting and office lighting, the issue of glare reduction receives much attention. Moreover, these luminaires are rather expensive and do not provide much flexibility in beam shaping.